FR2511427A1 - ACOUSTIC THERMAL MOTOR WITH STATIONARY SEALING DEVICES - Google Patents

Abstract

THE INVENTION CONCERNS AN ACOUSTIC THERMAL MOTOR WITH STATIONARY SEALING DEVICES. THIS MOTOR IS CHARACTERIZED IN THAT IT UNDERSTANDS AT A SELECTED FREQUENCY AND PRESENTING FIRST AND SECOND ENDS; A MEANS 42 FOR CLOSING THE FIRST END, A COMPRESSIBLE FLUID SUPPORTING A STATIONARY ACOUSTIC WAVE, LODGE IN THE CONTAINER; MEANS 14, 22, 24, 26 AVAILABLE AT THE SECOND END FOR CYCLICALLY EXCITING THE FLUID WITH A STATIONARY ACOUSTIC WAVE AT THE SAID SELECTED FREQUENCY; A SECOND THERMODYNAMIC AGENT 46 PLACED IN THE CONTAINER NEAR THE SHUTTER MEDIA, THE ENERGY MOVING TO THESE SHUTTER MEDIA WHEN THE MOTOR IS RUNNING. APPLICATION TO REFRIGERATION OR HEATING.

Description

The present invention relates to thermal engines and, more

  particularly, to acoustic heat engines whose sealing devices

are stationary.

  An important function of a heat engine is to pump heat from a thermal reservoir at a first temperature to a second heat reservoir at a second higher temperature, developing mechanical work. The Stirling engine is an example of a device. which, when used with

  an ideal gas, can pump heat backwards

  Such a motor has two mechanical elements, a working piston and an auxiliary piston, whose movements are mutually synchronized to reach one another.

  the expected result In an article entitled "Pulse-

  Tube Refrigeration "published in August 1964 in the" Trans-

  actions of the ASME "(pp 264-268), W E Gifford and R C.

  Longsworth describes an inherently irreversible motor

  They call it an oscillating tube refrigerator or a superficial heat pump refrigerator, which, in principle, only requires a movable element and makes the necessary synchronization between the temperature variations and the fluid velocity thanks to a delay of the contact. thermal input between a primary gaseous agent and a secondary thermodynamic agent

  (formed in this case by the wall of a stainless steel tube

  In place of a working piston, this device according to Gifford and Longsworth uses a rotary valve which cyclically connects at a frequency of about 1 Hz the tube to high pressure and low pressure tanks fed by a compressor L apparatus according to the present invention applies the principle of pumping surface heat, but it increases the operating frequency by a factor of about one hundred beyond the frequency of the aforementioned device.

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  motor of the invention does not include a compressor, but a trainer or acoustic exciter, thus dispensing with the use of all mobile devices for sealing and the need for external members with mechanical inertia, such as flywheels.

  One of the interesting features of the prior art

  This device uses a compressible fluid housed in a tubular container, as well as a progressive acoustic wave. The thermal energy is added to the fluid on the tube. one of the sides of a second thermodynamic agent and it is extracted from this fluid on the other side of said second agent The material interposed between these two sides is maintained in an approximate thermal equilibrium with the fluid, which forces a thermal gradient in this fluid to remain substantially stationary The operation of

  this device differs from that of the device of the invention.

  The known device uses mobile acoustic waves whose local oscillatory pressure p is necessarily equal to the product of the acoustic impedance pc and the local velocity v at each point of the motor.

  device according to the invention uses acoustic waves

  stationary conditions for which the p> pcv condition can be obtained in the vicinity of the second thermodynamic agent, thus increasing the ratio between the thermodynamic effects and the viscosity dissipation effects Mobile waves require that no reflection in the system occurs ; such a condition is difficult to obtain since the

  second agent is an obstacle that tends to -

  In addition, it is technically more difficult to obtain a thermodynamically efficient purely mobile wave system than a stationary wave system. In the invention of the reference cited above, it is also mandatory that The result is a close analogy with the Stirling engine. However, the requirement for the geometry of the fluid, necessary to achieve a good thermal equilibrium, necessarily requires that the primary fluid be in excellent local thermal equilibrium with the second agent. , together with the requirement that p = fcv for a moving wave, a significant loss by viscosity (except for unknown fluids whose Prandtl number is excessively low) The present invention takes advantage of the imperfect thermal contact with the

  second agent as an essential parameter of the process.

  Therefore, an engine according to the invention need not necessarily have the high viscosity losses of the moving-wave engine.

of the aforementioned US Pat. No. 4,114,380.

  U.S. Patent 3,237,421 (Gifford) discloses the superficial heat pumping device

  discussed in the aforementioned article by Gifford and Longsworth.

  The present invention is distinguished from that of this patent not only by the characteristics described above, but also by the fact that the regenerator, necessarily having to be interposed between the pressure source and the part of the apparatus of the aforementioned patent ensuring

  the pumping of the superficial heat is not essential.

  In fact, the incorpo-

  ration of such a regenerator in the engine according to.

  the invention decreases its yield as a result of the same problems of viscous dissipation of heat

  that affect the invention of the aforementioned patent US-

  In addition, the device of US Pat. No. 3,237,421

  requires a large compressor and requires

  While the engine according to the present invention is lightweight because it does not require such a compressor Finally, the engine of the Cifford patent also requires movable sealing devices, which

  is not the case of the engine of the invention.

  One of the objects of the present invention

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  consists in providing refrigeration and / or heating

  without necessarily providing sealing devices

mobile tees.

  Another object of the invention is to eliminate the compulsory presence of external mechanical inertia members, such as flywheels, which equip

  a refrigeration or heating appliance.

  The invention also aims at increasing the frequency

  operating frequency far beyond the frequency

  typical of most mechanical devices.

  According to the essential characteristics of the acoustic thermal engine of the invention, this engine comprises a tubular container, for example rectilinear, U or 3. One of the ends of this container is closed by a cap and said container is filled with A compressible fluid capable of supporting a stationary acoustic wave The other end of said container is capped with a device comprising, for example, the diaphragm and the oscillatory beam of an acoustic trainer or exciter for generating an acoustic wave at the In a preferred embodiment, there is provided an element such as a pressure reservoir for delivering a selected pressure to the fluid inside the container.

  thermodynamic agent is placed inside said

  container, in the vicinity but spaced from its closed end by a cap, so as to receive heat from the fluid that passes through it during the pressure increase phase of a wave cycle, and to yield this heat to the fluid when the pressure of the gas decreases during the appropriate phase of said wave cycle The imperfect thermal contact between the fluid and the second agent results in a thermal inertia interval starting at 90 between

  the local temperature of the fluid and its local velocity.

  This results in a temperature difference over the length of this agent and, in the case of the form of

251 1427

  preferred embodiment, substantially over the length of

  the shortest branch of the container shaped in 3.

  Heat sinks and / or heat sources may

  associated with the device of this invention.

  appropriate to cause refrigeration and / or

a heater.

  One of the advantages of the present invention is that it is easy to carry out, of simple design and

  inexpensive operation and maintenance.

  Another advantage of the present invention is that it does not include any mobile sealing device

  and presents a single and mobile element.

  Another advantage, specific to the present

  invention lies in the fact that it proposes a

compact and lightweight.

  In another of its advantageous aspects, the present invention may be used to heat or cool beyond or below selected temperature ranges, from cryogenic temperatures to very high temperatures, depending upon

  materials, pressures and frequencies used.

  The invention will now be described in more detail with reference to the accompanying drawing by way of non-limiting example and on which

  FIG. 1 is a section of a form of real -

  preferred embodiment according to the invention; and FIG. 2 is a transverse section, along the line A-A of FIG. 1, representing a second

  thermodynamic agent used in the form of

preferred embodiment of the invention.

  A motor 10 according to the invention, the preferred embodiment of which is illustrated in FIG. 1, comprises a cylindrical or tubular receptacle 12 of generally 3-shaped shape, comprising a U-shaped bend, a short branch and a long branch. is capped by a caster 14 of entralneur or exciter acoustic supported by a base plate 16 and fixed thereto by bolts 18 to form a pressurized fluid-tight seal between said plate 16 and said housing 14 In the preferred embodiment the base plate 16 rests on the upper face of a collar 20 protruding outwardly beyond the wall of the container 12. The housing 14 encloses a permanent magnet 22, a diaphragm 24 and an oscillating coil 26. conductors 28 and 30, passing through a seal 38 in the base plate 16, are connected to a source 36 of frequency current

  The set comprising the coil and the diaphragm

  is mounted by means of a flexible ring 34 on a support 32 secured to the magnet 22. It will be apparent to one skilled in the art that the illustrated acoustic exciter is of the conventional type. In the preferred embodiment, this exciter works in a range of

  frequency of 400 Hz (at least about 100 Hz) Any-

  time, in said preferred embodiment, a range of 100 Hz to 1000 Hz may be used in said form

  preferred, helium was used to fill the recipe

  12, but again it will be apparent to those skilled in the art that other gases (such as air and hydrogen gas) or liquids (such as "freons" or propylene) can also be readily used, even

  liquid metals like a liquid sodium eutectic-

  In one embodiment, a flange 40 is fixed, for example by welding, to the upper face of the short leg of the neck. An end cap 42, placed above the collar 40, is secured thereto by bolts 44 to form a pressurized fluid seal A second thermodynamic agent 46, which is shown in FIG.

  cross section in Figure 2, preferably consists of

  in concentric cylinders, in a spiral or in parallel plates made of a material such as "ylar" (terephthalic acid + ethylene glycol)> "Ny 1 on" (po 1 yamide), "Kapton" Cpolyiride ), an epoxide,

  a thin stainless steel or analogous material

  The material used must be capable of causing a heat exchange with the fluid contained by the container 12 Another solid material whose effective thermal capacity per unit area at the operating frequency is significantly higher than that of the neighboring fluid and which conveniently has a low thermal conductivity in the longitudinal direction, will act as a second thermodynamic agent. Small dots 56 illustrated in FIG. 2 may represent protuberances or other means for maintaining concentric cylinders, spiral windings or Parallel plates approximately equidistant from each other The presence of an extreme space between the cap 42 and the top of the thermodynamic agent 46 will be observed. In the vicinity of this extreme space and the top of the agent 46, the container 12 communicates. with a heat sink 50 via a conduit 48, thereby causing a n heat exchange by heat generation A second conduit 52, connected to the container 12 at the lower end of the thermodynamic agent 46, communicates with a heat source 54 and thus ensures an exchange

  thermal absorption by heat absorption A desired pressure

  selected or selected is issued by a source 64

  fluid supply under pressure, through

  of a conduit 58 and a valve 60 This pressure

  can be adjusted by a pressure gauge 62.

  The acoustic exciter, whose permanent magnet

  22 causes a radial magnetic field that acts on the current flowing through the oscillating coil 26 to provide the diaphragm 24 with the force to cause acoustic oscillations within the fluid, is mechanically coupled to the container 12 (acoustic resonator formed into a tube in 3 whose one end is closed by the cap 42) In a

  typical motor, the resonator can be approximate-

  long quarter-wavelength at its fundamental resonance, but those skilled in the art will understand that this feature is not essential. No mechanical-inertia device is required, since all the required inertia is provided by the primary fluid agent itself resonating at

  inside the tube in 3 The second thermodynamic agent

  that the layered layer 46 must have a low thermal conductivity in the longitudinal direction in order to reduce the heat losses. In the preferred embodiment, the spacing between the cylinders

  This concentric agent 46 is of uniform width.

  Another condition to be fulfilled by this second agent is that its effective thermal capacity CA per unit area is considerably greater than that (CA) of the neighboring primary fluid. These properties are mathematically represented as follows: C A CI d; C -C 2

A CA 2 C 2 2

  o C and C are the respective thermal capacities

I 2

  per unit volume of the primary fluid agent and the solid secondary agent 46 and 52 (2 1 1/2 being the thermal penetration depth in the second thermal diffusivity agent k 2, for an angular frequency C = 2 T f (f being the acoustic frequency) The condition that CA> CA is easily obtained, as well as small heat losses in the longitudinal direction, if the second agent is a material of the type "Kapton", "flylar", " Nylon ", an epoxy or stainless steel for frequencies of a few hundred hertz to a helium gas pressure of about 10.13 bar For efficient operation, it is necessary that the viscous losses are low This can be obtained if L /? c <1, or

  L is the length of the second agent and * is the length

  in radians of the acoustic wave represented by k => / 2 F = c / 2 rf (where c is the speed of sound in

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  the fluid agent) When sizing the motor,

  chooses a reasonable value of L, as well as a frequency

  Generally speaking, starting at L /> <1 For a L value of about 10 cm to 15 cm, a reasonable frequency is 300 Hz to 400 Hz for helium near room temperature. is then determined approximately by the mandatory condition JC Ok 9 1 necessary to obtain the necessary variations of temperature and the necessary harmonization between the temperature changes and the speed of the primary fluid 'T k then corresponds to the diffusion thermal relaxation time which ,

  when using a parallel plate configuration

  the, is given by XI:, = d 2 1 <2 k 1

  o k 1 is the thermal diffusivity of the primary fluid.

  In the presence of gas, the value of r is approximately inversely proportional to the pressure. The spacing of width d is then approximately determined by the inequality d 9 2 k 1/2 -25 A helium gas pressure of 10.13 bars gives perfectly reasonable values of d

that is, about 10 mm.

  These considerations are typical for the size

  With reference to FIG. 1, the operation is as follows: the acoustic exciter is placed in a housing to resist the pressure of the working fluid and is mechanically assembled to the resonator (tubular container 12 in 3). In a fluid-tight manner Electrical conductors leaving the oscillating coil are connected to

  the source 36 of audible frequency current through

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  The acoustic system was brought to a pressure p through the valve 60, using the source 64 for supplying pressurized fluid. The frequency and amplitude of the source of audible frequency current are

  chosen to produce the fundamental resonance corresponding to

  In a gaseous heel, an exciter such as "JBL 2482" manufactured by the company "James B Lansing Sound, Inc." will easily cause a pressure change. peak-to-peak ratio of 1.013 bar in the region of the end cap 42 when the average pressure in the container is about

, 13 bars.

  Since the length of agent 46 is considerably less than A, the pressure is almost uniform on this second thermodynamic agent.

  products are therefore substantially the same as those

  bare with an ordinary mechanical cylinder arrangement

  giving the same pressure variation at this high frequency. The pumping of the heat occurs in the following manner will be considered a small amount of fluid in the vicinity of the secondary agent at a time o the oscillation pressure is zero and becomes positive When this pressure increases, the amount of fluid moves towards the cap

  end 42 and its movement causes its heating.

  With a delay time Tek, the heat is transferred to the second agent from the hot amount of fluid after this fluid has moved toward the end cap beyond its equilibrium state, thereby transmitting the heat towards said end cap The pressure then decreases and, together, the temperature decreases Nevertheless, this temperature drop is not communicated to the second agent before the same amount of fluid has a significant distance from its state d equilibrium away from the cap 42 and towards the U-bend, then transmitting cold to this U-bend In these conditions, there is a global heat transfer from the bottom to the top of the space. The cooling of the bottom continues until the thermal gradient and the heat losses are such that the temperature of the second agent coincides with that of the neighboring fluid in motion when e

  Fluid moves An adjustment of the magnitude of.

  the extreme space below the end cap determines the volumetric displacement of the fluid at the end of the thermal inertia interval and, hence, plays an important role in determining the amount of heat pumped. will observe that, because its bottom is cold, the tube 3 shown has a good stability to gravitation compared to the natural convection of the primary fluid If a device

  according to the present invention is constructed for

  in a gravity-free environment, such as

  the space, the configuration in 3 of the tube becomes super-

  This configuration in 3 of the tubular container 12 may also be modified, as well as the behavior of the latter, if a significant drop in yield is

  acceptable For example, it is possible to use

tiline or U.

  The above description of a form of realization

  preferred embodiment of the invention has been presented for the purpose of illustrative purposes. It can not be

  considered exhaustive or as limiting the invention

  In view of its described form, and obviously, many modifications and variations are readily possible without departing from the scope of the invention. The embodiment shown has been chosen and described in order to clearly explain the principles of the invention and its practical application, so as to enable other specialists to best utilize this invention in many embodiments and with many modifications appropriate to the respective purposes sought. The scope of the invention is

  defined by the appended claims.

Claims (7)

  An acoustic thermal engine with stationary sealing devices, characterized in that it comprises a container (12) which, being able to resonate substantially at a selected frequency, has first and second ends; means (42) for closing off the first end of said container; a   compressible fluid capable of supporting an acoustic wave   stationary tick and housed in said container; means (14,22,24,26) disposed at the second end of said vessel for cyclically exciting said fluid with a stationary acoustic wave having substantially said selected frequency; as well as a second thermodynamic agent (46) placed in said container in the vicinity but away from said sealing means, whereby the energy is constantly moving towards said closure means when said engine operates.   2 heat engine according to claim 1, characterized in that it comprises means (48) for transferring heat from the container (12), in the vicinity of the closure means (42), to a well heat (50).   3 heat engine according to claim 1, characterized in that it presents means   (52,54) for cooling an external agent, in   effective communication with the container (12) in a region thereof located on the other side of the second   thermodynamic means (46) from the closure means tion (42).   4 heat engine according to claim 1, characterized in that the container (12) consists of in a straight tube.   Thermal engine according to Claim 1, characterized in that the container (12) has a U-bend. 6 Heat engine according to Claim 1, characterized in that the container (12) is J-shaped and comprises a branch short and one long limb.   7 heat engine according to claim 6, characterized in that the closure means (42) is disposed at the end of the short branch and the   excitation means (14,22,24,26) are located at - the end of the long branch.   8 heat engine according to claim 7,   characterized in that the second thermody-   Namique (46) is housed in the short branch.   9 heat engine according to claim 1, characterized in that the selected frequency is at least about 100 hertz.   Thermal engine according to Claim 1, characterized in that the selected frequency   is about 100 hertz at about 1000 hertz.